In a previous blog post we covered some of the benefits of pressure fermenting, and in this post we'll address some of the common questions brewers having regarding pressure fermentation to help you understand what you need to get going, and what you can do (or not do) to get the most out of using pressure fermentation for your next batch of beer!
What Is Pressure Fermenting?
What Do I Need for Pressure Fermenting?
- A fermenter capable of holding pressure - some popular options are Kegland's FermZilla and Keg-King's Apollo or Fermenter King/Junior
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| Keg King's Apollo range of fermenters are great entry level pressure fermenters |
- A spunding valve (to control/regulate the pressure within the fermenter) - like the Spundy or Blowtie.
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| The Blowtie spunding valve from KegLand is an excellent spunding valve for homebrewers |
Aside from these basic bits of equipment, you'll also need to consider how you're going to get your finished beer out of the fermenter and packaged - typically into a keg or bottles.
The aforementioned plastic fermenters don't have a tap/spigot, so pressure transfers are normally used to move the beer out of the fermenter, and all you'll need for this is a CO2 gas bottle, some liquid and gas disconnects and beer/gas line. You can read more about pressure transfers here.
How to Start a Pressure Fermentation?
Getting pressure fermentation underway is simple and very much the same as a regular fermentation. Here are the basic steps you'll need to follow.
- Ensure your fermenter is clean and sanitized
- Fill your fermenter with wort
- Pitch your yeast into the wort
- Put the lid on and seal the fermenter,
- Attach your spunding valve (usually to the gas post of the fermenter) - make sure you set/adjust it beforehand.
Pro tip: double and even triple check that you have put your spunding valve on the gas post and not the liquid/beer post. Attaching it to the liquid/beer post will see all of your wort drained out of the fermenter via the spunding valve as pressure builds in the fermenter!
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| Make sure your spunding valve is attached to the gas post to avoid losing all your beer |
Do I Need to Fill Headspace with CO2 Pressure?
A common question that comes up is whether the headspace of the fermenter should be filled with CO2 gas (from a CO2 bottle) after pitching the yeast and sealing the fermenter. It's ultimately a matter of preference, but there's no real benefit to be gained from doing this.
For those worried about oxidation, yes, there is oxygen present in the fermenter at this point, however once fermentation starts the yeast will begin producing CO2 that will expel all the oxygen out of the fermenter via the spunding valve, and oxygen is actually a good thing and required by yeast at the beginning of fermentation.
We've never applied gas to pressurise the fermenter prior to any of our pressure fermentations, however doing so is not likely to cause any problems either.
What PSI should I ferment at under pressure?
There's a few things to consider in order to answer this question. Generally speaking, a good starting point is 10-12 psi of pressure. Some people use more than this, which will lead to slightly more carbonation at the conclusion of fermentation, but it will potentially stress the yeast more.
Pressure fermenting does help to reduce unwanted off-flavours and esters which may or may not be desirable depending on what sort of beer you're making.
Another consideration is if you need to open your fermenter after fermentation has begun for dry hopping. If there's a large amount of pressure in the fermenter, releasing the pressure will often lead to the krausen expanding, rapidly, which is exacerbated if there's a large amount of pressure to release. The method I use is to start off fermenting at a low pressure (5psi or less) so there is less gas pressure to release to open the fermenter for dry hopping. Once this has been done the pressure can be increased to 10-12 psi.
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| You can dry hop under pressure by using a hop bong |
You can work around this though by dry hopping under pressure using a hop bong!
Do I Need a Spunding Valve If I Have a PRV?
PRV stands for pressure relief valve and is a standard inclusion on any pressure fermenter. It's role is slightly different to that of a spunding valve.
A spunding valve is used to regulate the pressure within the fermenter, so once the desired pressure (as set on the spunding valve) is reached within the fermenter, the valve will open and begin constantly venting the excess gas to maintain this set pressure.
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| Spunding valves like Keg King's Spundy should be used in conjunction with a PRV |
A PRV is primarily a safety device, and is used to ensure that the maximum rated pressure within the fermenter is not reached.
Ideally, a spunding valve and PRV should be used in conjunction with each other, so that if the spunding valve fails to vent the excess gas to maintain the set pressure, the PRV will take over and prevent excess build up of pressure within the fermenter which could lead to a catastrophic failure.
Using just one of these means there is a single point of failure which is rarely a good idea. Especially with most spunding valves on the market that attach to a ball lock post, which can easily become clogged/blocked with krausen or other matter during particularly aggressive fermentations.
So, the answer to this question is a resounding yes. You definitely need to still using a spunding valve even though your fermenter has a PRV attached.
What Yeasts are Suitable for Pressure Fermenting?
Yeasts that typically produce neutral flavours and characteristics are good candidates for pressure fermenting. Some examples are SafAle US-05 and Lalbrew BRY-97 and most lager yeasts due to the clean tasting nature of them.
Ale or other specialty yeasts that are used to impart unique flavours - like Saisons, or Belgian style strains are not good candidates for pressure fermentation as the pressure will typically suppress these unique flavours from developing.
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| Some yeast strains are better than others for fermenting under pressure |
To have the best of both worlds, you can have the spunding valve set wide open for the first few days of fermentation, since this is when most of these flavours are developed, and then close the spunding valve towards the tail end of fermentation to begin building up pressure within the fermenter. This is the method we use for most of our fermentations. You can use something like a RAPT Pill to monitor your fermentation in real time to take the guess work out and know exactly how far away the fermentation is from reaching the final gravity (FG).
Does Pressure Fermentation Take Longer?
No. If anything, pressure fermentations should be completed faster. This is because you are able to ferment at higher temperatures when fermenting under pressure.
What Temperature Should I Pressure Ferment At?
Another common question that has no real right or wrong answer. Personally we stick to the recommended temperature range for the sort of yeast that we're using, simply because we have a dedicated fermentation fridge so we're easily able to do so.
You can go higher as pressure fermentation suppress the off-flavours that are generally expected when fermenting at the higher end or even above the recommended yeast temperature range. But just because you can, doesn't mean that you should. If you have the ability to control the fermentation temperature then you should, but if you're not able to then make sure you're applying plenty of pressure in the fermenter to help control and reduce those off-flavours from developing.
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